Enhanced Image Display In Head-Mounted Displays

ABSTRACT

Methods and apparatus, including computer program products, implementing and using techniques for projecting a source image in a head-mounted display apparatus having a left and a right display for projecting a left and right images viewable by the left and right eyes, respectively, of a user. Source image data is received. The source image has right, left, top, and bottom edges. The source image data is processed to generate left image data for the left display and right image data for the right display. The left image data includes the left edge, but not the right edge, of the source image and the right image data includes the right edge, but not the left edge, of the source image. The right image data is presented on the right display and the left image data is presented on the left display.

This application is a continuation of patent application Ser. No.11/580,580, filed Oct. 13, 2006, which is hereby incorporated byreference herein in its entirety. This application claims the benefit ofand claims priority to patent application Ser. No. 11/580,580, filedOct. 13, 2006.

BACKGROUND

A head-mounted display (HMD) is a display device that a person wears onthe head in order to have video information directly displayed in frontof the eyes. HMDs are also known as near-to-eye displays. A HMDtypically has either one or two small CRT, LCD or OLED displays withmagnifying lenses and other associated optical elements. The display(s)and optics are typically embedded in a helmet, glasses, or a visor,which a user can wear. Lenses and other optical components are used togive the user the perception that the images are coming from a greaterdistance, which reduces eyestrain. In HMDs that use a single display,the image is typically projected through optics that split the imageinto two identical images, and redirects each image to the respectiveeye. With two displays, the HMD can show stereoscopic images. Thestereoscopic images attempt to create depth to the images by simulatingthe angular difference between the images viewed by each eye whenlooking at an object, due to the different positions of the eyes. Thisangular difference is one of the key parameters the human brain uses inprocessing images to create depth perception or distance in humanvision.

Some HMDs can be used to view a seethrough image imposed upon a realworld view, thereby creating what is typically referred to as anaugmented reality. This is accomplished by reflecting the video imagesthrough partially reflective mirrors, such that the real world is seenthrough the mirrors' reflective surfaces. The augmented reality can becombined with the stereoscopic images in various types of applications.Some examples include applications in surgery, where radiographic data,such as CAT scans or MRI imaging can be combined with the surgeon'svision. Military, police and firefighters use HMDs to display relevanttactical information, such as maps or thermal imaging data. Engineersand scientists use HMDs to provide stereoscopic views of CAD schematics,simulations or remote sensing applications. Consumer devices are alsoavailable for use in gaming and entertainment applications.

FIGS. 1A-1D show some exemplary schematic views of different HMD displayarchitectures. FIG. 1A shows an example of a transmissive HMD displayarchitecture. In this architecture, a white light source, such as awhite LED illuminates a liquid crystal display (LCD) that displays animage to a user. The image is then relayed to the user's eyes through anoptical system, which can be either an aspherical or diffractive lenssystem. Such lens systems are well known to those of ordinary skill inthe art and will also be discussed in further detail below.

FIG. 1 B shows an example of an emissive HMD display architecture. Inthis architecture, the display is an Organic Light Emitting Diode (OLED)display, and thus a separate light source can be avoided. The image isthen relayed to the user's eyes through an optical system, similar tothe system described above with respect to FIG. 1A.

FIG. 1C shows an example of a reflective HMD display architecture. Inthis architecture, the display is a Liquid Crystal on Silicon (LCoS)display. In LCoS, liquid crystals are applied to a reflective mirrorsubstrate. A light source, such as a white or RGB LED directs light ontothe LCoS display. As the liquid crystals in the display open and close,the light is either reflected from the mirror below, or blocked. Thismodulates the light and creates the image. The image is then relayed tothe user's eyes through an optical system, similar to the systemdescribed above with respect to FIG. 1A.

FIG. 1D shows an example of a Micro-electro-mechanical (MEM)/Laserdisplay architecture for a HMD. MEM devices are micro devices havingelectro-mechanical moving parts that are capable of constructively anddestructively interfering with an incident light source to produce oneor more optical signals. Optical MEM devices are typically fabricatedfrom Silicon-based materials using lithographic techniques. Some opticalMEM devices have reflective ribbons that are formed over a suitablesubstrate structure, such that the ribbons are spatially arranged inparallel and are coupled to the substrate structure. In use, a portionof the reflective ribbons are moved by applying an operating biasvoltage, or switching voltage, across the ribbons and the substratestructure. By alternating, or switching, the potential of the biasvoltage, the ribbons are alternated between the positions forconstructive and destructive interference with the incident light sourceto generate optical signals. Other types of MEM devices use differenttypes of movement, such as rotating, bending, or translating thereflective elements. As can be seen in FIG. 1D, the light source is alaser, and the resulting optical signals from the MEM devices aredisplayed on an image surface and viewed by the user.

Whereas the majority of these HMD configurations work well for theirintended purposes, there is a continuing need for improved HMDs.

SUMMARY

This invention relates to processing and displaying images in ahead-mounted display. According to one embodiment, the inventionprovides methods and apparatus for providing a wider field of view andcreating a more natural viewing situation for a user of a head mounteddisplay, which results in improved comfort and usability for headmounted displays. By using larger displays inside the HMDs andrecreating each image displayed on each display as each eye wouldtypically see it, a wider field of view and increased viewing comfort isachieved. Various embodiments of the invention allow users to customizedifferent viewing parameters of the head mounted displays to accommodatefor individual user variation in the users' eyes.

In general, in one aspect, the invention provides methods and apparatus,including computer program products, implementing and, using techniquesfor a head-mounted display apparatus for a user. The head-mounteddisplay apparatus includes a left display, a right display and aprocessor. The left display projects a left image viewable by a left eyeof the user, and the right display projects a right image viewable by aright eye of the user. The processor receives data representing a sourceimage, which has a right edge, a left edge, a top edge, and a bottomedge. The processor processes the data representing the source image togenerate left image data for the left display and right image data forthe right display. The left image data includes the left edge but notthe right edge of the source image and the right image data includes theright edge but not the left edge of the source image. The processorpresents the right image data on the right display and present the leftimage data on the left display, and as a result a wider view is createdthat results in improved viewing comfort for the user.

Advantageous implementations can include one or more of the followingfeatures. The processor can receive data representing the source imagefrom an external source. The external source can be a portable sourceand can include a memory in which the source image is stored. The headmounted display can include a memory in which the data representing thesource image is stored, the memory being operatively coupled to theprocessor. Each of the left and right displays can provide a horizontalfield of view for the user that is greater than about 30 degrees. Eachof the left and right displays can have an aspect ratio of 16/9. Datarepresenting the source image, the right image data, and the left imagedata, can be movie data. Each of the left and right image data caninclude a centerline of the source image. The centerline of the sourceimage can be displayed to the right of a centerline on the left display,and the centerline of the source image is displayed to the left of acenterline of the right display. One or more light sources can belocated in close proximity to a perimeter of each of the right and leftdisplays to dynamically show colors matching the colors that aredisplayed on the right and left displays, respectively, so as to enhancethe viewing experience. A user interface can be provided that includesone or more controls for providing instructions from the user to theprocessor about what portion of the source image to include in thegeneration of the right image data and the left image data,respectively.

Embodiments of the invention can be implemented to include one or moreof the following advantages. One advantage is that the translation of aright image to the right and a left image to the left provides a widerfield of view and increased viewing comfort compared to conventionalHMDs. Another advantage is that users can make individual adjustments oftheir HMDs to fit the distance between their eyes, and so on. As aresult of having two images that are slightly translated in thehorizontal plane with respect to each other, stereoscope-like effectsmay also be achieved, which further increases the viewing comfort of theuser, and enhances the user's experience.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features andadvantages of the invention will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1A-1D schematically show some exemplary display configurations inHMDs.

FIG. 2 shows a schematic view of the placement of the displays relativeto the user's eyes in a HMD with two displays in accordance with oneembodiment of the invention.

FIG. 3 shows a schematic view of a HMD image generation system (300) inaccordance with one embodiment of the invention.

FIG. 4 shows a flowchart of a process for displaying two horizontallyoffset images in a HMD in accordance with one embodiment of theinvention.

FIGS. 5A-5C show some schematic views of aspherical optical arrangementsfor use in a HMD in accordance with one embodiment of the invention.

FIGS. 6A-6C show some schematic views of diffractive opticalarrangements for use in a HMD in accordance with one embodiment of theinvention.

FIG. 7 shows a schematic view of a laser system that can be used withHMDs in accordance with various embodiments of the invention.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The invention will be described in detail with reference to specificimplementations including the best modes contemplated by the inventorsfor carrying out the invention. Examples of these specificimplementations are illustrated in the accompanying drawings. While theinvention is described in conjunction with these specificimplementations, it will be understood that this description is notintended to limit the invention to the described implementations. On thecontrary, the description is intended to cover alternatives,modifications, and equivalents as may be included within the spirit andscope of the invention. In the following description, specific detailsare set forth in order to provide a thorough understanding of thepresent invention. The present invention can be practiced without someor all of these specific details. In addition, well-known features ordetails may not have been described to avoid unnecessarily obscuring theinvention. In order to fully appreciate the properties of the variousembodiments of the invention, some concepts relating to the human visionand image science research will be explained.

Field of View (FOV):

The field of view for an image describes the angular extent of theimage, that is, the amount of a given scene that is viewable in theimage. The human eye has a 180-degree field of view, and typically theimages projected on displays in HMDs only show a much smaller field ofview. This is largely due to the limitations of the lenses and displaytechnology that are used to record the image. Various embodiments of thepresent invention, as will be described below, provide mechanisms formaximizing the FOV for the images, to make it as close the FOV of thehuman eye as possible.

Eye Motion Box (EMB):

The eye motion box represents the area in which the user's eye can movewithout loss of the full FOV. Having a sufficiently large EMB is one ofthe most significant parameters relating to the viewing comfort of theuser. A typical EMB is about a 10-15 millimeter square.

Image Focal Plane:

The plane is where an image is focused. Typically, having an image focalplane located far away is more comfortable, since it minimizes thestrain on the accommodation muscles in the eyes. Strain on these musclesis thought to be related to myopia, that is, near-sighted vision.

Eye Relief:

The eye relief is the offset of the nearest optical surface from theeye. The optimal eye relief distance, is typically considered to be thedistance at which the exit pupil is approximately the same size as theeye's pupil. The optimal eye relief distance is usually in the range ofabout 18-30 mm. Using an exit pupil smaller than the observer's pupilmay force the user to press his or her eye close to the eyepiece inorder to see an unvignetted image. Alternatively, using an exit pupillarger than the observer's pupil at a comfortable viewing position,results in wastage of light and a dimmer than optimum image.

Peripheral Vision:

Peripheral vision is a part of vision outside the very center of gaze.There is in actuality a very broad set of non-central points in thefield of view that is included in the notion of peripheral vision. “Farperipheral” vision exists at the edges of the field of view,“mid-peripheral” vision exists in the middle of the field of view, and“near-peripheral”, sometimes referred to as “paracentral” vision, existsadjacent to the center of gaze. Peripheral vision is good at detectingmotion and as a result, occluded peripheral vision in HMDs can cause auser to experience motion sickness symptoms.

A particularly useful application for the HMDs in accordance withvarious embodiments of the invention lies within the entertainmentfield, namely viewing movies. FIG. 2 shows a schematic view of a HMD(200) in accordance with one embodiment of the invention. As can be seenin FIG. 2, the HMD (200) has two displays (202; 204) that are situatedsuch that a centerline (206) of each display (202; 204) is offset with adistance d, typically about 0-4 millimeters, from a centerline (208) ofthe user's eyes (212 a; 212 b). This allows the displays (202; 204) tocover more of the periphery of the user's field of vision. As is shownin FIG. 2, preferably, the centerline (206) of the left display (202) islocated a distance d to the left of the centerline (208) of the user'sleft eye (212 a), and the centerline (208) of the right display (204) islocated a distance d to the right of the centerline (208) of the user'sright eye (212 b). Optical components (210 a; 210 b) focus the imagesfrom the respective displays (202; 204) onto the user's eyes (212 a; 212b) at a comfortable viewing distance. However, placing the displays(202; 204) off center without performing any additional imagemanipulation will confuse the brain of the user, as each eye is lookingat a different portion of the image when the user looks straight ahead,and the brain is expecting to see essentially the same image with eacheye. Therefore, the centerlines of the respective images shown on theleft and right displays (202; 204) should be matched or almost matchedwith the centerline (208) of the user's eyes (212 a; 212 b). How this isdone will now be described with reference to FIG. 3, which shows aschematic view of an image generation system (300) in the HMD, and toFIG. 4, which shows a flowchart for the processing and display of anincoming video signal.

As can be seen in FIG. 3, the system image generation system (300)includes the left display (202) and the right display (204), a processor(306), and a memory (308). The processor (306) is connected to thememory (308), which contains instructions for how to process imageframes contained in an incoming video signal (310), which represents amovie to be displayed in the HMD.

As can be seen in FIG. 4, the process (400) for displaying the twooffset images starts by the processor (306) receiving an image frame ofthe movie (step 402), shown as “Video In” (310) in FIG. 3. The imageframe can be received from an external video source, such as a portablevideo player connected to the HMD, or even through a wireless connectionto some external video source. Alternatively, the memory (308) in theHMD can contain one or more previously downloaded videos that can beaccessed by the processor (306) in the same way that a video from anexternal source is accessed.

The processor (306) then divides the received image frame into a leftimage to be displayed on the left display (202) and a right image to bedisplayed on the right display (204) (step 404). In one embodiment thisis done, for example, by duplicating the incoming image frame into twoimage frames—one for the left display (202) and one for the rightdisplay (204).

Next, the processor (306) determines a horizontal translation isdetermined for each of the right and left images (step 406). Thishorizontal translation is illustrated in FIG. 2 as the distance dbetween the centerlines (206) of the respective displays (202; 204) andthe centerlines (208) of the image frame. In the embodiment shown inFIG. 2, the distance d is the same for both the left display (202) andthe right display (204), but it should be noted that individualtranslations can be determined for each display using the sametechniques. In determining the amount of translation d, the processor(306) uses software instructions that are stored in the memory (308). Asis well known by those of ordinary skill in the art, there are manysoftware programs that can control where to display an image or movie ona display. Some examples include Final Cut Pro®, available from AppleComputer Inc. of Cupertino, Calif., and Adobe® Premiere®, available fromAdobe Systems of San Jose, Calif.

Some embodiments take the user's interpupillary distance (IPD) intoaccount in calculating the of translation d for the right and left imageframes. For example, the user can either input a numerical valuerepresentative of his IPD, if it is known. Alternatively two sampleimages can be displayed to the user, and the user can dynamically changethe horizontal translation of the pictures by moving a dial, or someother control, until a comfortable viewing configuration is obtained.Similar techniques can also be used to make adjustments based on theuser's peripheral vision, since the peripheral vision typically variesfrom user to user.

After determining the translation amount d, the processor (306) directsthe left image frame to the left display (202) and the right image frameto the right display (204) in the HMD (step 408). The process thendetermines whether there are any more image frames to be displayed (step410). If there are additional image frames, the process returns to step402, and if there are no more image frames, then the process ends.

As was discussed above, there are a wide variety of displayarchitectures that can be used in HMDs. The principles discussed abovewith respect to FIGS. 3 and 4 can be applied to any of thesearchitectures. Each of these architectures comes with its particularadvantages and drawbacks. For example, the LCD microdisplays shown inFIG. 1A have high brightness, good color saturation, good imagesharpness and have a low manufacturing cost, but they also exhibitso-called “screen door effects.” Screen door effects occur when thedisplay is enlarged to the point that the user's eyes can distinguishthe individual pixels and thus a grid pattern in the image on thedisplay. LCD microdisplays also suffer from inherent size limitations inthat the manufacturing yield is lower as the displays get larger, andthus the cost of the displays increases.

The OLED microdisplays shown in FIG. 1 exhibit low power consumption,require simple optics, have high contrast ratio, and have a lowmanufacturing cost, but they have limited lifetime and their brightnessdecreases over time. They may also have potential problems withresolution and pixel consistency.

The LCoS microdisplays shown in FIG. 1C have a high pixel density andcontrast, fast response time, IC compatibility and are experiencing anincreasing application in rear projection TVs (RPTVs). On the otherhand, there are currently some concerns about their lifetime, theysuffer from color break ups that create “rainbow effects.” LCoS displaysuse what is typically referred to as field sequential color lighting.That is, the pixels in the LCoS display turn on and off in order toreflect or not to reflect light. Thus, in order to get an image, red,green and blue colors are sequentially flashed onto the LCoS panel. TheLCoS panel is coordinated with this and creates the image by having theappropriate pixels turn on or off. The three color sequence happens sofast that the user's eyes cannot distinguish the individual colorsduring normal viewing. However, if the user moves his eyes across theimage quickly, this effect is visible as a rainbow, thus the namerainbow effect. In addition, LCoS displays also require more complexoptics and the color saturation is poor.

The MEM/laser system shown in FIG. 1D provides infinite focus, thewidest color gamut among these systems, and is relatively small. On theother hand, it requires fast modulating lasers, and there may be powerconsumption and/or safety issues, depending on how the HMD is being usedby the user.

What is true for all displays used in the various HMD embodiments inaccordance with the invention, however, is that they are generallylarger than the displays that are used in today's conventional HMDs.Typically the size of the displays in various embodiments of theinvention is larger than about 0.7 inches diagonally across the display.The effect of having larger displays compared to conventional HMDs isthat the image fills the entire field of view for the user and make useof the user's peripheral vision, similar to what the user experiences ina Imax or Omnimax movie theatres. Another side effect of translating theimages is that a stereoscope-like effect is obtained, in which the userperceives the images as having greater depth than what is currentlypossible in conventional HMDs.

The displays can also have different aspect ratios depending on theprimary application of the HMD. For example, an aspect ratio of 4×3,i.e., similar to a television screen, may be desirable by a user whoprimarily is interested in using the HMDs to watch television programs,whereas an aspect ratio of 16×9, i.e., similar to a movie theatrescreen, may be desirable by a user who primarily is interested inwatching feature films.

The above discussion has been focused on the image generation system andthe displays of the HMD. Another important component of the HMD is theoptics (210 a; 210 b), which actually transforms the image on thedisplays into an image that can be viewed by the human eye. A briefoverview of various optical arrangements that can be used in accordancewith various embodiments of the invention will now be described.

Aspherical optical arrangements include various types of prism and/orlens arrangements. FIGS. 5A-5C show some examples of aspherical opticalarrangements that can be used in HMDs in accordance with variousembodiments of the invention. FIG. 5A shows a coaxial arrangement of aset of lenses arranged along a common axis. The lenses bend the incominglight to create a virtual image at a comfortable viewing distance forthe user. The coaxial arrangement is simple and low cost, but may bebulky and have problems with spherical aberrations, and provide a smalleye motion box. FIG. 5B shows a concave mirror arrangement, which alsocreate a virtual image, but also folds the optical path. The concavemirror arrangement is a simple and low cost arrangement, but it requiresa fair amount of space and the alignment between the elements iscritical for the arrangement to work properly. FIG. 5C shows a freeshaped prism arrangement, in which the image from the display isredirected and magnified. This arrangement provides a large field ofview and is compatible with a wide variety of display devices, althoughit may be somewhat more bulky than other optical arrangements describedherein.

Diffractive optical arrangements include various types of arrangementsthat bend and spread light. FIGS. 6A-6C show some examples ofdiffractive optical arrangements that can be used in HMDs in accordancewith various embodiments of the invention. FIG. 6A shows a light-guidedoptical element (LOE), which can be made of planar transparent glass orplastic. The LOE configuration increases the eye motion box for a givenimage and can be made as thin as about 2 mm. The LOE is see-throughcapable and provides a large field of view (up to about 40 degrees), andcan also be encapsulated into a larger lens, if need be. The LOE can beused together with LCD and LCoS displays.

FIG. 6B shows a binocular light-guided optical element (BLOE), which canbe made of planar transparent glass or plastic. In the BLUEconfiguration, a centered input image is directed to binocular images.It is important that the left and right images are properly aligned inorder not to cause physical distress for the user. Just like the LOE inFIG. 6A, the BLUE can be made thin, typically about 3 mm thickness, andis see-through capable. It can be used together with LCD and OLEDdisplays.

FIG. 6C shows a wedge display. The image enters the edge of the wedgeoptics, and travels through an expansion region before it is displayedto the user's eye. Its thickness can be as small as about 2 mm, and itssize can be very large—up to 50-inch prototypes have been manufacturedto date. It is also possible to use in a folded design, which may savespace compared to other optical arrangements, and it accepts a widevariety of display types.

FIG. 7 shows a schematic view of a J.4EM1Laser System that can be usedin HMDs in accordance with various embodiments of the invention. TheMem/Laser system uses red, green and blue lasers with a single or dualMEM device to generate raster-scanned images. At present, the horizontalscanning rate is about 31 kHz and the vertical scanning rate is in therange of about 0-400 Hz. Of course, these parameter will change as newtypes of MEM elements and lasers become available. One advantage ofMEM/Laser systems is that they have an infinite focal distance. As aresult, one can create an image on a flat surface at any distance, andthe image will be in focus. A limitation of the system is that as thesurface is further away, the image gets dimmer.

The various embodiments described above have been focused onconfigurations using two displays. However, it is also possible to use asingle display, provided that the display is sufficiently large (or canbe modified by the optics to appear that way) that it fills the entirefield of view for the user. Alternatively, a smaller single display canbe used, and optics can be provided that splits this single image into aright image and a left image to be displayed in front of each eye of theuser at sufficient magnification. As the skilled person in the artrealizes, in these situations, there is no need for the processor tomanipulate the display image from the source, as was described abovewith respect to FIGS. 3 and 4. The actual horizontal translation of theimage occurs in the optics that split the image into two separateimages. It should also be noted that the above described principles canalso be implemented in HMDs that use more than two displays. In suchimplementations, the amount of translation for an image shown on aparticular display would be calculated based on the physical location ofthe display relative to the other displays in the HMD.

In some alternative embodiments, the images are not horizontallytranslated by the processor (306), but instead sufficiently largedisplays are provided so that the field of view for each eye is filledand the limitations as to what the user can view is determined by his orher physical constraints. That is, the user's eyes rather than thedisplay sizes limit the field of view. Alternatively, this can also beachieved by changing the optics associated with the display, such thatthe image is magnified more than in today's HMDs and give the user theappearance of looking at a large display.

In some embodiments, the periphery of the displays can be additionallyequipped with light sources that dynamically project light that matchesthe images that are shown on the displays. This configuration canfurther enhance the user's viewing experience, since it uses more of theuser's peripheral vision. Such a configuration is described in theco-pending U.S. patent application Ser. No. 11/580,774 entitled“Peripheral Treatment for Head Mounted Displays,” filed concurrentlyherewith, Attorney Docket No. APL 15 OO/P4249US 1, which is herebyincorporated by reference in its entirety.

In some embodiments, the HMDs described above can also be equipped withan audio system, such as a set of headphones or some other type of audiodevice. This will allow the users to watch feature movies and/ordocumentaries essentially anywhere and without having to worry aboutconventional issues, such as screen glare, and so on. Furthermore, theuser experience in viewing movies using HMDs in accordance with variousembodiments of the invention can be as good, or even better, than what auser experiences in a movie theatre.

The invention can be implemented in digital electronic circuitry, or incomputer hardware, firmware, software, or in combinations of them.Apparatus of the invention can be implemented in a computer programproduct tangibly embodied in a machine-readable storage device forexecution by a programmable processor; and method steps of the inventioncan be performed by a programmable processor executing a program ofinstructions to perform functions of the invention by operating on inputdata and generating output. The invention can be implementedadvantageously in one or more computer programs that are executable on aprogrammable system including at least one programmable processorcoupled to receive data and instructions from, and to transmit data andinstructions to, a data storage system, at least one input device, andat least one output device. Each computer program can be implemented ina high-level procedural or object-oriented programming language, or inassembly or machine language if desired; and in any case, the languagecan be a compiled or interpreted language. Suitable processors include,by way of example, both general and special purpose microprocessors.Generally, a processor will receive instructions and data from aread-only memory and/or a random access memory. Generally, a computerwill include one or more mass storage devices for storing data files;such devices include magnetic disks, such as internal hard disks andremovable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM disks. Any of the foregoing canbe supplemented by, or incorporated in, ASICs (application-specificintegrated circuits).

To provide for interaction with a user, the invention can be implementedon a computer system having a display device such as a monitor or LCDscreen for displaying information to the user. The user can provideinput to the computer system through various input devices such as akeyboard and a pointing device, such as a mouse, a trackball, amicrophone, a touch-sensitive display, a transducer card reader, amagnetic or paper tape reader, a tablet, a stylus, a voice orhandwriting recognizer, or any other well-known input device such as, ofcourse, other computers. The computer system can be programmed toprovide a graphical user interface through which computer programsinteract with users.

Finally, the processor optionally can be coupled to a computer ortelecommunications network, for example, an Internet network, or anintranet network, using a network connection, through which theprocessor can receive information from the network, or might outputinformation to the network in the course of performing theabove-described method steps. Such information, which is oftenrepresented as a sequence of instructions to be executed using theprocessor, may be received from and outputted to the network, forexample, in the form of a computer data signal embodied in a carrierwave. The above-described devices and materials will be familiar tothose of skill in the computer hardware and software arts.

The present invention employs various computer-implemented operationsinvolving data stored in computer systems. These operations include, butare not limited to, those requiring physical manipulation of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. Theoperations described herein that form part of the invention are usefulmachine operations. The manipulations performed are often referred to interms, such as, producing, identifying, running, determining, comparing,executing, downloading, or detecting. It is sometimes convenient,principally for reasons of common usage, to refer to these electrical ormagnetic signals as bits, values, elements, variables, characters, data,or the like. It should remembered however, that all of these and similarterms are to be associated with the appropriate physical quantities andare merely convenient labels applied to these quantities.

A number of implementations of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. A head-mounted display apparatus, comprising: a left display that displays a left image; a right display that displays a right image; and a processor operable to: receive a numerical value representative of interpupillary distance; receive source image data; determine a first horizontal translation for the left image based on the numerical value; determine a second horizontal translation for the right image based on the numerical value; and generate left image data for the left display and right image data for the right display based on the source image data, the first horizontal translation, and the second horizontal translation.
 2. The head-mounted display apparatus defined in claim 1, wherein the processor is operable to: after receiving the source image data, divide the source image data into a left image frame and a right image frame.
 3. The head-mounted display apparatus defined in claim 2, wherein the first horizontal translation is a first distance between a centerline of the left display and a centerline of the left image frame.
 4. The head-mounted display apparatus defined in claim 3, wherein the second horizontal translation is a second distance between a centerline of the right display and a centerline of the right image frame.
 5. The head-mounted display apparatus defined in claim 1, wherein receiving the source image data comprises wirelessly receiving the source image data from a portable source.
 6. A head-mounted display apparatus, comprising: a left display that displays a left image; a right display that displays a right image; a dial that is configured to be moved by a user; and a processor operable to: receive source image data; determine a first horizontal translation for the left image based on the position of the dial; determine a second horizontal translation for the right image based on the position of the dial; and generate left image data for the left display and right image data for the right display based on the source image data, the first horizontal translation, and the second horizontal translation.
 7. The head-mounted display apparatus defined in claim 6, wherein the processor is operable to: after receiving the source image data, divide the source image data into a left image frame and a right image frame.
 8. The head-mounted display apparatus defined in claim 7, wherein the first horizontal translation is a first distance between a centerline of the left display and a centerline of the left image frame.
 9. The head-mounted display apparatus defined in claim 8, wherein the second horizontal translation is a second distance between a centerline of the right display and a centerline of the right image frame.
 10. The head-mounted display apparatus defined in claim 9, wherein the centerline of the left image frame is aligned with the user's left eye.
 11. The head-mounted display apparatus defined in claim 10, wherein the centerline of the right image frame is aligned with the user's right eye.
 12. The head-mounted display apparatus defined in claim 6, wherein the first horizontal translation is the same as the second horizontal translation.
 13. The head-mounted display apparatus defined in claim 6, wherein the first horizontal translation is different from the second horizontal translation.
 14. The head-mounted display apparatus defined in claim 6, wherein receiving the source image data comprises wirelessly receiving the source image data from a portable source.
 15. A head-mounted display apparatus, comprising: a left display that displays a left image; a right display that displays a right image; and a processor operable to: receive interpupillary distance information; receive source image data; and generate left image data for the left display and right image data for the right display based on the source image data and based on the interpupillary distance information.
 16. The head-mounted display apparatus defined in claim 15, wherein the processor receives the source image data from an external source.
 17. The head-mounted display apparatus defined in claim 16, wherein the external source is a portable source and includes a memory in which the source image data is stored.
 18. The head-mounted display apparatus defined in claim 15, wherein the processor receives the source image data wirelessly from an external source.
 19. The head-mounted display apparatus defined in claim 15, further comprising: a memory in which the source image data is stored, the memory being operatively coupled to the processor.
 20. The head-mounted display apparatus defined in claim 15, wherein the interpupillary distance information comprises a numerical value representative of interpupillary distance. 